During drilling operations from just after initial spudding of a well through completion and initiation of production, drilling fluid or drilling “mud” fills the interior of the formed well bore. Some types of muds are petroleum-based materials. Petroleum-based materials comprise at least 90 weight percent of an oil-based mud (OBM) as a continuous phase. Examples of suitable base petroleum materials include crude oil, a distilled fraction of crude oil, including diesel, kerosene, asphalt, waxes, lubricating oils, mineral oil, and heavy petroleum refinery liquid residues. Typically, a minor part of the OBM comprises water or an aqueous solution that is in the mud as an internal phase. Such water-in-oil emulsions are useful to transport chemicals that are not otherwise useful in the continuous phase. Other optional OBM components include emulsifiers, wetting agents and additives that give desirable physical properties to the mud or treat the well bore wall.
Oil-based muds also include synthetic oil-based muds (SOBMs). Synthetic oil-based muds are crude oil derivatives that have been chemically treated, modified, altered or refined, or combinations thereof, to enhance and promote certain chemical or physical properties and exclude other aspects of typical OBMs. SOBMs are monolithic systems that behave in a manner as if they were an OBM but provide a limited and predictable range of chemical and physical behaviors. In comparison to a distilled fraction of crude oil, which may contain several classes (for example, alkanes, aromatics, and heteroatomics) representing thousands of individual compounds, a SOBM usually comprises one class representing at most tens of individual compounds (for example, ester compounds in a C8-C14 range). Examples of useful materials for the base fluid of a SOBM include linear alpha olefins, isomerized olefins, poly alpha olefins, linear alkyl benzenes and vegetable oil- and hydrocarbon-derived ester compounds.
A mud with an aqueous continuous phase—a water-based mud (WBM)—typically comprises water in a range of greater than 50% to about 99% water. Unlike OBMs, WBMs may have a significant portion of hydrocarbons, including materials that would normally serve as the basis for an OBM, as part of the WBM. The base fluid for the water-based systems include fresh water, natural and saturated salt waters, natural or artificial brines, sea water, mineral water, and other potable and non-potable waters containing one or more dissolved salts or minerals. In regions where water is scarce or environmental regulations do not permit the disposal of untreated formation water, recycling recovered formation water from other production sites can provide an inexpensive source for a WBM, especially if the formation water contains salts and minerals that are useful to stabilize clay and shale downhole.
Besides salts and minerals, often other additives are useful in attempting to control the viscosity or inhibition of water-based mud. Common additives include sodium or potassium silicates (“silicate muds”) to inhibit shale and seal microfractures that occur during drilling, quebracho (“red mud”) and other tannates, ferrochrome lignosulfonate (“lignosulfate mud”), potassium, formate, lignites, phosphates, polyphosphates, gypsum, water-soluble polymers (“polymud”), lime, cellulose and xanthose based polymers, biopolymers, brines, biocides, corrosion inhibitors, foamers and cleaners.
The ability to maintain rotational velocity and fluid flow is a significant attribute of all drilling fluids, but this is especially true when the drilling tools stop their rotation and their introduction/withdrawal movement. Fluid momentum and disturbance of the fluid flow within the well bore by the tools permits suspension of solids, incompatible with the continuous phase liquids and gases to be maintained throughout the course of the drilling fluid flow pathway from the surface, downhole, and then back uphole for recovery and reintroduction. Reduction of fluid momentum due not only to general fluid friction but also friction against the sidewalls and the downhole equipment eventually causes the drilling fluid to settle. To prevent this settling, often it is necessary to continue pumping to the surface or slowly rotating the drilling string to keep the drilling fluid moving to a point where solids do not drop out of the continuous phase and incompatible gases and liquids do not separate.
It is desirable to include with a drilling fluid a composition that can significantly lower the frictional effects of the drilling fluid such that fluid momentum may be maintained with increased ease by action of the drill string or pumping of the drilling fluid to and from the surface. Such a composition would not only provide safer and more predictable operations with the modified drilling fluid, but also energy usage would be significantly reduced. A composition that is also environmentally friendly and that is biodegradable is also advantageous for use in marine and ecologically-sensitive environments.